YII~'a 'a~ PEBIMENTEB - ietlabs.com · ton. Tllc output filter fu rther reduces the lUlrmonie...

"" ... ::c ..... CI z: ... '" ..... z: ... ::IE ... "" = '" ... ... ::IE

YII~'a 'a~

~ PEBIMENTEB VOLUME XVI No.5 OCTOBER . 1941

A VACUUM·TUBE·DRIVEN TUNING·FORK OSCILLATOR

.41Ao IN THIS ISSUE

P,,8<' hll'I>I:>.o.N(: "; BIt,nc f. S

ASS !;IIII' . f.!) i'HO.II L.o.ROIIA1'OHY P ARTS - P A HT I V . 4

MOIIII: 1:<I' t"O R.II.o.TI O l" . P"K~ ;< F.! 6

VIlf.Q U II:NCY Monu,",,· TIO'Ol • • 7

.THE ELECTRO · MECHANICAl OS C III A TOR, whose frequcn cy is controlled by a tuning fork , has many uses in clcc lri('al comlll il n ica lions. The TYPE 813 Oscillator a nd its prclieceS60r lhe Tn>E 21 3 have been uscd, for ins lan('c, as po\\ er soun-es for bridgc measuremcnts and for transmission measuremen ts on lines and cables, as moduluting sources for t('s t oscillators and rUllio-bcacon trunsmilters, and as tcst · tone soun:es for communication systems.

For applications where a constan t .frc(llIcl1cy 8u(lio oscillator is needed for permanent installation in other equipment or circui ts, the tuni ngfork t ype is usuall y the mOSlcconomica1.

The TYI'E 813 Oscilla tor, like its predecessor l he T\"PE 2 13, is a microphone.butlon.driven lype. For some applications. in pllrticular those requiring very 10 ..... dis tortion, stabil it y of output voltage, or a-c operation, vacuu llI-tulle drive is morc satisfac tory. To mee t these r C(luirclIlc nts , the new TYPE 723 Vacuum-Tube Pork . showlI in Fi gure 1, has Lee n designed. This ins t.rument has extremely low distortion so that it clin

he used fordiSlortion j measun' rnc nts witll-ou t add i tional fil ters, and it s output is much more s ta ble

r iGUllt: 1. Vic,,' o r the 'I'l l'!; 723 Vac" um.T"I." Oscilla tor , showing the pauel.

IET LABS, Inc in the GenRad tradition

534 Main Street, Westbury, NY 11590 www.ietlabs.com

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GENERAl RADIO 2

L-4

B- B+

FICUlu~ 2. Functional circu it t1ing ruUl or the T VI' v. 1'2 3 V lteuum·Tube Fork.

Ihan th a t of the microphone·\'ullo ll I ~ ["le.

The tuni ng fork ;ti;(' lf is illcnLica\ '" it b tha i UliI.' I\ in the TH'E 8 13 Oscill a tor . Fig " ure 2 sholls t he declrieal circu it. Driv ing coils L~ " nd L~, "oUlltl o n L ./iha l)C>d l)Cr · mane nl lllagncl.S to gi ,-c a COIISlant polariza tion. an' a rra nbrcll along o lle lillc of tile forI.. . aliI I @i rnila r coils '''1 a nd [fl.,

fuci ng the o lher ti nt.'. 8(' f li' as piekup ,"oils. \ I \ SC. t} pe ,aCllum lube pro\ illes Ihe nCI-es;;;ary nmplifica t.ioll 11eIIH.'e1l piekup a nd dri, ing ci rcuits. The output fi lte r is in ser ies " ilh the ([ri vi ng coile and feeds an ou tput lra nsrorlnc r . . \ I appetl S(-'('ond ar) \\ inding pro. ides out· pU l ill1l'cd an("(!s o f 50. 500, and 5000 ohms.

T he '1', I'E i2:~ \ r uellHln .Tuhe rork is lI \ a il able in 1.H, models. ] OOO c)clcs 1ITl(1

100 cycles, and \\ ith e ither of t\\ O lypes of 1)O\\'cr suppl}, bllllcries, or an a.e 1)(1\(('r pack. The no(: po"'cr unit uses seleniulII rectifiers lind incl udes a voltage regul a tor tu be to miuimi ze thc c ffcct of linc volt age fluc tuations. Thc two power s"pplics arc iUlerchlUlgcablc llIechuni. call y and mOllnt in thc oscill a tor cabine t as sho\\ II in Figure 3.

BC('IHISC lIluglic tic tlri .e luul pid .up ~ impose comparllti .. c1y lilLIe res train t lIpon Ihe vilJr ll. tion of the fo rk, t il l' fre· fluency 81,abilil )' and waveform of this oscillator lire consitlerabl) be tte r th an th ose o f mi croph one·button.d ri vcn L) pes. and the e ffec ti \e Q of the fork is higher . Another (Ilctor contribut ing to lOll dis tortion is the grea te r degree of lincuril )' obtllin ablc i ll the operntioll of a vacuum lnbc tlwn in a microphone but·

FICORlt 3. Vie"'e sbowing 111,. l)(Iwer.~upply coll1l,artnU!1I1. Left. hlHlery !ul)ply unU. rIght. s-c power elll,!,ly.



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ton. Tllc output filter fu rther reduces the lUlrmonie ampli ltilles, so that the lotal

r- IlarmOllie content iii less Iban O.5o/t wilen Ihe oseillalor is o j:lCra lcll into a IOlid equa l to or g.realcr thal1 the nOlninal 0111.·

pul impcdallee. Tl lc rated outpuL is 50 milli wlI llS inl.o

3 EXPERIMENTER

11 mal.t:hed resistive load. The fork, thc tuLe, alld the associaLCJ circuit {' ]clnents are mounted on the ull. le .. sillc of a bakeli te ('lInel. The walnut cabinct in cludes s pace for the pOller suppl y.

SPECifiCATIONS

F rl que ney : Thc TYPE 723 VacuuIII·Tuhe Fork it f U(lplied for t .... o Ol>(lratiug {re<llJcl1ci~"iI. 1000 cyeleil wnd 400 cyeleil. (Sec price li$t below.)

Frequency Stab Illly: The te"'I'eralure coe(· lident of frequenoy iii HI'llroxirIJately - 0.00lJ<, per dcpree Fallrenheit. !'he frequency ;iI en · tirely Indtlpendcnt of load illl\..,d"nce. '~hen tbc aoe I)()wer li"l'l'l y ;S UilOO. an initi,,1 down. wwrd dnft of frm~uency occurs 116 the tcmper· alure of tbe fork '8 ufft"(!led hy hellt "euerated in the l)(Jwcr,~ul'ply unil . Tlui tolsl frequ ency d rift i6 oCthe oroJer of .15% tl').2 %. -'lust o£t.hi~ uri h , howe .. er, occurs ill the fo rst 30 lIl;lIut.C/I of op<::ral;ou. Ace u ra cy: The frequency i. adjusted to wilhill :1::0.01 % of iLl! 51NCi6cJ vulue, II I 77" Fahren . heit, IIsiug butt'lry (lower ~"Iljlly. Output : The oull'ut to II matched loat! is ap. proxiluately 50 "UJliwattii. Internal Output Im pe dit nc e:Outl'''t imped. ance" of 50, 500, atld 5000 OlUnd ure provided . Waulorm and Hum Lnel : The tOlal lmr. llIonic content is leM than 0.5 %. Tloe h"m i6 II CJ; ligible. Term i nal s: Bindluslvostil for IhcoUl l'lI1 cir· cui t are ,uolJoted on the panel. Hattery ter· minals arc hrvught ou l. to "unk"'n scre .... heads on

Ihe Ililnd t o pcrmit oneusurements of the Iml· tery voltagOi. Power Suppl y: The instru,"cnl i~ lI\uilphle for cither huth:ry ol,eraliou or for operation from 105 to 125,volt, 50 10 60-<'ycle hue. 1'0r h3tlery ollllrul iou one Hur"e;!s h ' IOI; 41"" (l H ,"oIl ) a"d ''''0 U\lrg~ type '7,30.~ (45 ... oh) lire retl"ired. The hHllerillll uud /I.e 1)(J,,'cr Slll!I,ly ure illterclillngcuble. Tbe l)(} .... er SUl' l'l r. Tn' ¥. 723·PI, is a .. ailuhlc Reparately. (See pncc list. ) The ON.OFf switch iii urra llgml to conlrvl Ihe a.e line or .he butlcry currenl-Vacuum Tubes :

For battery supl,ly: I tYl>C IA5t: .I-'or a.esul,,)ly: type IA5G

I t y/Ill VII ·t05·30 The n~"CeI!Illiry tuuCil ure SUllplk..J.

Acc essories Supplied: A scvC,,·fOOllioe conn0010r cord is SUI'I,t ied ",ith the n·c Ol)erllt e<.l mooe!. M 0 u n II n ( : The Q;lCillator lI!l1lcmhly ;~ mOllnted on a hakeli tc pund ... ,,,1 is Il nelOl,..d in a walnu l cubinet. Dlm .nslons: ( Length) 1 0~{ X (width) 6 H X (heighl ) 7~ inches. over. all. N e I We Illtl: 1114 1)QlIml ~. includiug battcriCfl; U pollnd~ 14 ounces. ,,·illo a-C KUPllly; a.e I""wer sUI'I,ly alonc, t l_..{ IIQU II\Ia.

1Y/Je Frcqm:nc)' Power S" l'l'ly COOt! Word Price

723-A lOOO cydCll Ballerie!! S~A KE $70.00 723-C 1000 cycles lOS to 125 "olt;:;, so ... !) "'.00

50 to 6Q cycles 123-U -100 cydes Hatteries STOHY 7V.00 723-0 -100 cycles 105 to 125 vol!.!!, SU LKY 90.00

50 to 60 eyelet. 123-1'1 A.COr erate\IPowcrSulll'ly Only . , . ...... SNA K.E\· UoI.TT 22.00 723- 1'2 Sctol {eplacement l:lutler;~'11 ............. SNA""YI'\ CK 2,00

NOTE TO EXPEDITERS To insore an early repl y 10 follow-up inquirica 0 11 ulidelivered orders, plea~'

Slate in your inquiry the order number, tbe date of the order, and, if apace permits, tlte Ulll tcrial ordered . Thi s iuforma tiOll \\ ill assist us ma lcrially ill locR t iug aud tracing }our order.



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GENERAL RADIO 4

IMPEDANCE BRIDGES AS SEMB LE D FR O M LABORATOR Y PAR TS

PAR T I V-T RAN SF 0 R MER ERR 0 R S

eTHE IDEAl SH IELDED TRANS · FOR MER interposed L,etl' cen a geller ntor RUlI hrid ge " ould provide complete isola tion be tween the two \\indiogs. exct' pL for Ihe desired illlluc Li vc coupling. E\'c n in a carefull ) Jcsigllcd alld cuns tructed lruusfOTmcr. ho ... ·e\'e r. then: '" ill he sollie small rcsillual electrO!> la lie and leakage couplin g he .... H:c ll the " ind ill!,"5, which ,,-ill ;JllrollUt.:e ex lrunCOWI

voh age!! into the Lritlge circuit. Thi s type of error may best he allulyzcJ by COllsillerillg the e ffec t o f introoucing (acr0ll8 lIny arm of a hridge) all cx lf' rnal \oll age £ ' in series " illl a n im pt:tlancc Zr. 3.S illustra ted in Figure 1. The c llua

Liun uf balance for this network is

z,' _ Z, z,(~)

(Z: ) ZAZ.v+ ~

• ( I)

T he parame ter P is gi\cn h}

~ -1 ± .(1 +~:) .

" 1",- " .... ,_. "e ., ...... , ..... e 00", r.. .he c.ooe of. _I""",d.nce _., ..... ....... ..-.-., .... at lini '~ .... _

r.d ... ,,,,,- ~ ........... {lJ .... r .. iII I ...... e". boll ,bo- u, .. --... ... /1 '-'0,_ ,.-., .'''''1,...,. ... 1.

DET£CTOR

It will be observed that the balance Equation (2) iij identical to that \\' hich .... ould be obtained if a passive illl l)la l llllt.'t'

equal LO Z, ~

,,'cre counec ted in pura l-

lei with ZN. This fuct makes it possible to cS Lilll Ulc n 'l,dily lhe effec t o f II lra} coupling from the voltage source to the bri(lgc .

Oy properl y choosillg the magnitude am] 1)()larity of E' the expression for {j

call lie redu(.'tJ LO zero (for 1\ given val ue

Z of the rutio ~) . Under this condit ion

no er ror \\ ill be caused by the prCSClIl,;C of Zr. as it will cffccti,'c1y appear 8 S an in finite impcdam.:c <l CTOSS ZN' Ln Fi gure 3 is prcscnlcll 'lII ex pe rimental \'crificu tion of this fal' t. The o lJserveci chall gc ill power-fac tor readi ng of a '1"'1'£ 716-"Capacitance UriJge is plolted against the computed ,' aluc of the paramc ter (J for various val ues of £ ', T hcoro.:tically, this plot 8ho liid be a s traight lim:, pU811 ' ing through lhe origi n, o f IIlope erpllli to the coupli ng resis tullce nT • Tilt: agreement obtained is we ll wi thin t he limit of experimeut.al error .

ll1 the prac tical case where £' is the voltage source supply in g the brill se, the rutio a is the e ITec ti ve voltage ratio of the bridge lransfo nner. Thus from the poini of \ iew of reducing the e ITeet of residual interwinding cou pling, there ill an 01" timum tUrIIS ratio for any gin!!! l;riJge. In general , of ('ourse, othe r oonsirlera ·

F'CL' RI> I. Showill j; 8n e~l crll a l vohllga COil · """" ncctctI IIcrOl<8 " 1" 1IIg .. IIr... through lin iUl '

I,cd l nee Zr.



TEL: (516) 334-5959 • (800) 899-8438 • FAX: (516) 334-5988

DETECTOR

". ". ric-- E, ----'h

0 ,

GEIt[RATOR

FIGUlu~ .2 .. Showi,!g how on irnpedal\c~ be· ' .... oon wln,lrngll of a rYI'1> 578-A Sh.eJd ....... l r""s · for mer gin'!! ri;Jf) to the Sitnlltiotl 8ho .... n in

Figure I.

tion s dictate the choice of tllrn ~ ralio, but it is well to keep in mind thai there is a best choice of PQ{urity.

Usiug the TYl'E 578-A Shielded Transformer in the urid ge arrangements previously described, the residual coupling between windings efTee li vely places a slUall ca pacitance ({jCT ) in parallel with

NT large resis tance {j across one of the

capucitum;c arms o( the bridge . This call be seen by com paring Fig

ures 1 ami 2. Wiu, the bridge groumled at the jl ct"o f tb ·t III ' I no e capaci anee arllls, the asci CT , HT ,

though high sid ollliary

Ilator voltage E', ill series \\'itll is placed across the N arlll. AI-there is sollie coupling frOIll tbc e of the primary to ei ther sec-terminal, Ihe olll y pa tll shown

"' is to til to the se negligibl

terminal which oondary shield .

e in comparisQn.

is COil lice ted The other ;,

""GUliS 3 I'olioll fae resJl.ond~ rneailured

. Plot of observed change in diui. tor all a function of fj. The 610llC cor· to a resi! tance of 226 'ncgohm~. The do{:: valuo of the coUlllin!; rl'llis ll1nCe

Ullt. ........ aft 221 megoh"" .

5 EXPERIMENTER

The ca pacitance CT is of the order of a fe\1 tenths of a micromierofarad , while the d·c leakage resistance is of the order of 10,000 megohms or b .... eater. In addition to the doc leakage. there is a COIn

IlOnelit of resis tance con tributed by the dielectric losse~ associated wi th CT. At 1000 cycles this componClH is roughl y of the same magnitude as the leakage re sistance. A t frequencies much belo\\' this, the latter COlll llOnent is more importa nt, while at higher fre(lueocies Ihe djeleetric losses in Cr become the significant cOIllIJoO nen t.

In the previously sugges ted arrangellIent of the Seheri llg circuit the t1n -

Z T . peda!H:e Ii IS placed across P, or lin-

knowil arm of tbe bridge , aod becomes part. of the zero capacitan(."C and tliss;pation fac tor oC that arm. Since ~ varies with the SCLijug of the ratio arms, however, t his comllOnent is 1I0t COIlSlant, and the value of Csot and Dsat will 110t be the same fo r a ll setti ngs of the ratio

A arms. For \.lrge val ues of B a Cairly

large capaci lancc is added , but in this case the unknow n (C,.) is large and the error remains negligible.

r II the series-resistance bridge as de-ts.... A"I"" .IId s.~''''Q'-. 19·11 , &fN"i"""'~, .

.. .. .. f-

I .. , f- .. f- --I

0 -0

.,

- ,. , O. M

t-r" I r -P:

1 I

-



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GENERAL RADIO 6

Zr !!Cribo,'ll. {i ,,, plac:-ed :u:ross t in: V, or

alll uJ anl Il rlll o f the bridge. "here it is cOlllplt' l,cI} negligihle if fj fl'lIIa ill li n'll'

1I011uL1) slIHlll, since eN - JO,OOO p.p. f.

In the e.'l:trcUlC ClI se, ho\\clc r , of

U ,ceilla] to l(){){l, a capal'itatwc of the

or.ler of 25 JJj.l f \\ ill be plUlXfl a"fOa.;

1 c.v. i. c .. i3 - 1 ± I (1 + 1000) . Ahhough

" mall O'om pa rcd to 10,000 p./o' f .

this va lue is Ilo t ncgligibll" UuL II 'a luc

U of A cquul to 1000 corrcs llOlHls tv 1\

eu pal' il 3lH'C in 1I1t~ P arm o f onl ) 10 j.!1lf.

Thus lhe error of 25 pafls in 10.000 in · LroJuceJ c;orrCS I)Oud ;; 10 onl~ U (1.1 \ '

hundredth!! of a micromicrofarad ;n till' dc lcfmiuuLioll of tbe unknQ\\ 11 capacitance.

Similar arg Uluc n LS \,.11 11110 \\ that l he

1/ , cfTl'cl o f - is gCllcrllll,' Jlc"li<tihle to p •• olher sources of error. a l 1000 C) clcs. For ex treme \ aluell of br i,l~e arm impedances. hOllever. it is In·llto estimate the

II , e ffec l o f (Je T and ""i for an) gil en meas-

ure ment I.efort· II 8tllte men l. of accuracy is made.

I( the vollage;; E' lind Il:o are no t in (or 1800 Ou l of) phuS(' the rutio a Le -

comes I,:o mplex. The imped unce

ill the n no long:t· r of the same character as ZT, and the jJrc~llI;e of a coupling ca pal.:itancc. which normally affects o nly the I.'apacitlllu:e halance , will rrOllucc a shifl. in dissipation factor 1, ;118. 11 (,'('. Similarl y, a rcsisllInce coupling: wi ll affect tile ca pacitancc Ollluncc. This call otcur a ill ig-her freque ncies, "here t he leakage reactance of Ihe IrllllsforIHcr becomcs appreciable. pro.:ltlcill~ a phase shift bcl\l ceu input and oulput "oltages.

- !v ...... G. K \ STO '

MORE INFO RMATION , PLEASE ! • TIM E--a particularl) valuable , ·UIII ·

modil ) to defense industries - CAli fre()lICUll ) I.IC saled "hell I':quillm"1IL is rt' tll rne,1 for repai rs if an efforl is madc 10 s up"l) our ~n-il.'e Dt' par tmclIl \'lith lle tai led informalion on Ibc ImulJle e:\ · l)Crie ll,·cll .

Of len instrumcnls hllve h.~e ll re turned \'lith 11 0 I;rCIlIC[ troubl,' 1111111 .. hlo\\ 11 fuse or lltl t.crioruted .... (I(·uu!U lube. Ol', ·a.~ ioll a ll )' ellUip"II'UI hns been rc tu rncu iu rirst-d".,~ cOlhlitioll LeI·aIlSo.' II II' opcr a ting: inSlnu-tion" suppJicu \lilh il hud not 1K.'C1i fo llo\'lell, or l}(h,sihl ) \lert: 1I0l

full ) IIl1dcrs tOOl I. Frequentl) \\ bat a ppcar., 10 be lIusa tiafae tory lJoCrformam;e ca n be traced to tbe ex tcrnal ('ircuit II ith

"hieh the insl rUIIlCllt is IJ.' ing used. The ull for ttlll ll ie as pec t of such eases

iii Ih at ollr S iandllrdi zing Lahoratory must spcUlI l,;ollsideraLle tiute ill cheel..· lug these rc turned i"SlrulIlcnLS to mal..e s ure thai there are no otucr sources of difficulty and no intcrm.iW' nt trouhles \lhieh ma r he lyi ng: dorlllnu t only 10 re"ppc ur a t Ihe custome r's la lJOral.ory . If these checks fC\ ('31 110 cvi denl'c of faul I y operation \'I e nu,SI the ll \lrile the customer for informution \\lIich might he t· h: r have l)Cell furll islll'd earlier lIud m ighl even ha \I.' e lim ina lell Ihe lIeot:ssi l) for re turning Ihe C{I"ip"H' lIt, the reb) saving time, illcon\t· uic nee. and expense.

E'en "hell C(luil'lIIeut is u('luall) in



TEL: (516) 334-5959 • (800) 899-8438 • FAX: (516) 334-5988

lIee,1 of repairs, a JeLailed s tatcmcnt of tht' IrQuble may he very helpful. Anal· ~6is of Ihis infurmation someti mes shows Ihal the trouble is "aused h) a single defecti\'c eOIlJI}(lncn t "hich ,'an be cas· il y replaced. Where time is imporl.ant. this partean he su pplied 10 Iht.: etlslolllcr "ilh illS lrudiolls for its installation ill the ills trullIt' nt. If. 0 11 Ihe other ham\. the equipment IUUSt be returned , our laboratory \\ ill at least know what condition Il t:ells eorrection. find no lilll t.: will be lost in makin g elt:tra prcliminary eheck!.. Sincc repair charges tlcpcnd ul}(l1l the cost of the labor and malerial in· volved. a considerablc sa ving can I hilS be IlIIHle in till! repair charge.

A further advantage of the detailed report is that it eliminate!> Ihe possi. bility of our overlooki ng an intermittent fault \\ hilc somc otber J"feet is Iliseov. crf'd and eorrccted,

Tllc following procc(llire is recom· _ IllcmlCtl whcll trouble appart.:nLly de·

"clops in General Hadio equipment; ( I) Stud y tht.: in struc tion book carl;·

fully . (2) Check all fuscs. (3) Check all billleri;.:!! ulltier normal

load. He plaec if tht.:y sllo\\ less than ratetl voltages. If LWllcril's are ol d. it is advisable to try a lIe\\ sct, because Ihe inlemal rcsistanl.'e lUa} he high enough to eause trouble withollt showing II ;;cri ous drop in \'ollagl'.

FREQUENCY • BY NOW almost I~"t.: rront' has felt the ;mpllel of 1111' Na tional Defcnse Program in one way or anuther, For man y manufac turers. including the Gencrnl Hallio Com pany. it. has InClill 1 (I corn · plete rf'arrangCIlIt.:llt and expu n;:.ioll of

7 EXPERIMENTER

( 1) C hcd. all tubes. (5) Check earcflllly the ex teTIIlI1 cir·

cuit with \\hieh it is being ui'CII, par· lieulurl y if the cirellit is a lIelY onc.

I f Ihc SOIlr('e of trouble cannot be 10· ('at..·d, write IHir Service Dcpartlllt.:l1l, giving the t) pc 111111 Ef·riaillumbcr of the inSlrUllIen l, II Jes('ril' tion of tht.: exact !littur .. of the ddee!.. telling " 'hether il developed sudden I) or Over a pe riod of lillie. (\lui II dingr:lIn of t he circuit connecteJ to il sho\\in g COIllpOllcnt va lues :JIltl loc:ltion;:; of grouIHJ;;. Wbcl) meas. uring iustruments. such as bridges or me ter,;. give inal:C1Ir:l\c readings. a s heet of sample .lata anJ a Jt·slTipl.ion of lhe tlW t hod of 1I1caSIII'ClllCllt ",houltl he gi\'(~ n. Whcn Ihe instruc tion boo!. givcs sC H'ral para h'Ta ph!! under thc titles o f INSTALL \TI0N aud OPE HATI ON. ;t is (81)(>1';1I11) helpful LO describe the oLS("rvl'd effect!! of carrying 011 1. the eon_ :>I'cul.ive Step;; in each paragraph .

L pon the reL'Cipl of this ;nl'orlllnl;OIl t.he Scrvi,';e Departlllellt "ill Ix- in a po. sition to render prompt aiOSis tallce :lIld

can advi!'oc you at once how yOllr service problem CUll I*st Ix- h:lIIll1eJ,

WheTl repairs arc 10 hc mafic nn in. "trlllll('Tlts llt'cdt'J in Ihe execlltion of a Natiollal Dcfello<c conlrad. the \\/Jrk ca n ~ greatl y fncilitule,1 if Illc l)I"de rellcc rating ifllllent.tOlwd in Ihe repair order.

- KII'LII"G AUA\lS

MOOULATION manufacturing faci litics, -:\lost of our pinos for nc \\ CQlliplilClll. eSJ'lI'I·jall y for llolHlcfensc malerilll , have Lecn completely changeJ , allIl "" are pUllin~ 11IIr Illax inllllll effort il1l,o Ihl' prOiluction of urgen II y rcquirc(1 dcfcullC 811 pplies.



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GENERAL RADIO 8

One of the non-dcfense activities that we have been especia ll y loa th to postpone is the produc tion of ins trument s fo r broadcast frC(llIcncy mOOulatiolJ .

Designs had been comple ted alli l production \\' IIS well under way for II mod· uia liolllllonitor for I'M I,ransmillers 81l.J for a s tam.lard-signal ge nerator fo r F~ I

broad cast. rCL'eiver t.es ting. We bclit' vc that both of these ins truments arc designed to cover adcl.lu8lel ) the rC(llliremcuts of their s l>ccia l field s, and uuder ordinary cirClUnslan(:cs the), .... ou ld have been on the market some lime ago. T he manufacture of I.hem has had to be put aside. al leas t ICmporaril y, but we arc glad to sny that "" C art' ahl.~ s till 10 con· tinue engineering dc\'clopmcllt of illlpro \'ed circuits and JIlc thotls; in the end, of oourl!e, we intend that the instru· ment s shall be up to the llIinul(' wheu they are finally released.

Another ins trulIlent that is hei n:; (Ie· vclorlCd in the labora tory is 1\ frequcnc) lIIonitor for F\1. and this work wi ll be con tin ued up to the IlOin1 of produc tion 60 tllllt we can s tart it immedi a tel y when production facilitiel! a re again availlible.

These arc examples of thc work that is continuuusly goi ng 0 11 in our Illhorll· torics. !\tany of our engineers arc work· ing on instrtllllcnts dircc tl y connected \\'ith the defense prohrra m, but a parl of tllC s taff is continuing the llevelopmcl1 t of more ge nerall y uscIu! e(lu ipmcnl. As has hapl.It' nell be forc in a situation of this kind. the gn ·at couoollt rated effor t on 1l1ilitllry eq uiprnent \\ill result in a Lig step forwa rrl for the t,'(i llununica tions art in general. nnrl all lines of rad io develop. mellt \\' ill eveutually receive the benefits of the thi ngs that arc being learned in doi ng the defense job.

- \. E. 1'IIIES." .,,,

ABOUT THAT SHOTGUN SHELL We IU"'e received II number of CO UJ1l1ent5 from readers about Fi gure 3 of the

article 00 the Microfiash aIJpcaring in las1 mon th's Experimellter. T he ca pt ion is undoubtedly incorrect, !lud the slre ll was fired from the right, of tire pic turu.

THE General Radio EXPER IMENTER is m.ailed withollt charge each month ' 0 engineers , scientisl s, l ecll,licia,u, (111(1 o t/l crs intcrest.ell in

communiootio'l·jrefJuency met.I.'iUrernent, an.d contrul problems. ,,11' cn sendillg reflu ests for s llbscriptiollS (H,d uddress · clwllge no ticeR, "If.>flse supply Ol e following informat.ion.: ,wme, compuny Hom e, com[Jlluy ad· d ress, type of business company is engaged in, and title or position. of individual.

GENERAl RADIO COMPANY 3D STATE STREET CAMBRIDGE A, MASS ACHUSETTS

BRANCH ENGINEER ING OFFICES

90 WEST STREET, NEW YORK CITY

ttli NORTH SEWARO STREET, LOS ANGElES, CALIFORNIA



TEL: (516) 334-5959 • (800) 899-8438 • FAX: (516) 334-5988

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